1. Field of the Invention
The present invention pertains to a device for the automatic centering of cathodes in eyelets for cathode tube electron guns.
2. Description of the Prior Art
One technology for fixing the electron gun cathodes of cathode tubes uses "eyelets" which are substantially shaped like sleeves flared on one side, the flared part ending in a collar. This collar is fixed to a supporting electrode set just behind the first grid of the gun. The cathode is inserted into this eyelet and can move freely inside it. The said cathode is held at the end of a hollow rod connected to a vacuum tap. This rod is generally called a "central electrode". When the distance between the active side of the cathode and the first or second grid is set at the desired value, the cathode is welded to the eyelet, generally by spot welding, at three or four spots.
However, despite all the care that might be taken in fixing the eyelets, they often have positioning errors such as displacements in translation or inclination with respect to the theoretical axis. Faults of this type adversely affect the correct positioning and setting of the cathodes, and could damage the cathodes when they are inserted in the eyelets or when the instruments used to place them are withdrawn.
3. Summary of the Invention
An object of the present invention is a device which can be used, when the cathodes are being automatically positioned in the eyelets, to compensate for errors in the positioning and alignment of the three cathode eyelets of an electron gun. This device also enables the forward and backward movement of the cathode in the eyelet to adjust the distance between the cathode and the first grid of the gun, practically without any gap between the cathode and its eyelet.
The device according to the invention has a "central electrode" fixed to a support, which is movable in the direction in which the cathode is set, by means of a flexible or floating bearing, the rear part of this said central electrode being connected by a joint to a pusher which is movable in the same direction as the support but is capable of being actuated independently of the said support. Should the central electrode be hollow, it is advantageously connected to a vacuum tap.